Astaxanthin is a very good antioxidant from the carotenoids family. It is more stable and potentially more efficient than the better known lutein and zeaxanthin. Astaxanthin is the pink pigment in krill, in lobster, in pink flamingos.
I use it for over a year now, both before sport, and also when needed, on day one of POIS, when pre-pack as not stopped all the symptoms. I use the BioAstin brand, and only takes 4mg doses a day, but not on a regular basis ( as you may know, I always go for very safe dosage).
It has no side effect at all for me, and is good for energy level.
More info, if interested, at
https://examine.com/supplements/astaxanthin/Also, a recent 2016 study showing astaxanthin improves cognitive performance in mice following mild traumatic brain injury:
https://www.ncbi.nlm.nih.gov/pubmed/28048972 . This neuroprotective effect can be beneficial in POIS, according to my vision of part of POIS being due to an immune-caused inflammation in the brain, causing emotional and cognitive symptoms.
The company website, at
http://www.nutrex-hawaii.com/bioastin-hawaiian-astaxanthin , is a little too enthusiastic, so I prefer more objective sources
Lots of research are going on on this antioxidant. Note that krill oil has asthaxantin as one of its main active principle, and is not unlike omega-3 fatty acids + Astaxanthin. So articles about krill oil are also partly about astaxanthin, like
https://www.ncbi.nlm.nih.gov/pubmed/24667135 .